Process for the removal of mercaptans from petroleum distillates with an aqueous alkaline reagent containing lignin and the regeneration of the spent alkaline reagent



Patented Mar. 15, 1949 PROCESS FOR THE REMOVAL OF MERCAP- TAN 8 FROMPETROLEUM DISTILLATES WITH AN AQUEOUS ALKALINE REAGENT CONTAINING LIGNINAND THE REGENER- ATION OF THE SPENT ALKALINE REAGENT Robert R. Hibbard,Lorain, and Franklin Veatch, Cleveland, Ohio, asalgnors to The StandardOil gohrlnpany, Cleveland, Ohio, a corporation of N o Drawing 10 Claims.

This invention relates to the treatmentoi' hydrocarbons to remove sulfurconstituents normally present, and has specific reference to the removalof mercaptans from petroleum distillates.

The treatment of petroleum distillates, such as gasoline, to removesulfur compounds stems from the objectionable character of suchcompounds, particularly from the standpoint of odor. It is desirable to"sweeten" the distillate by removal of sulfur constituents in the nature01 free sulfur, hydrogen sulfide, mercaptans and thio compounds eitherby conversion to less objectionable suliur-containlng compounds, or byactual removal from the petroleum distillate.

It has long been known that sulfur compounds can be extracted from ahydrocarbon distillate to a great extent by washing with an aqueoussolution of alkali, such as caustic soda. The more acidic compounds suchas hydrogen sulfide go into solution readily, and their removal presentslittle problem.

Petroleum cllstillates commonly contain mercaptans in concentrations offrom 0.001 to 0.1%, expressed as weight percent of mercaptan sulfur. Themercaptans are weakly acidic, and are often only partially removed bythe alkali wash, so that the amount of mercaptans remaining present inthe petroleum distillate is above the critical limit for a so-called"sweet gasoline. This may be explained by the following equilibriumequation oi mercaptans in a hydrocarbon distillate treated with anaqueous alkali solution:

+M H RSH RSH T: Its-+11 RSM V Dissolved in Dissolved in Ionized inSaponiiled hydrocarbon (l) alkali (2) alkali (3) in alkali It will beapparent that the concentration of m'ercaptans in the hydrocarbon phasecan be kept at a desired low level if the equilibrium (1) is shifted byrendering the mercaptans more soluble in the alkali phase, or bymaintaining a low concentration of mercaptans (either ionized or asmercaptides) in the alkali phase.

It has been proposed heretofore to facilitate mercaptan removal fromhydrocarbon distillates by the addition of compounds to the alkalisolution which renders the mercaptans more soluble therein, and thenremoving the dissolved mercaptans when the alkali solution is spent" orApplication April 18, 1946, erlal No. 683,237

(Cl. lac-29) has absorbed mercaptans to an extent that itsmercaptan-removing action is lessened. The latter has been accomplished,for example. by stripping the mercaptans from the spent alkali solutionwith steam, by treating the alkali solution with a solution of elementalsulfur or polysulfldes, by oxidizing the mercaptans with air, and byother known methods of mercaptan separation. The rate of oxidation ofmercaptans in spent alkali solutions by treatment with air can beaccelerated by adding suitable catalysts to the solution. Metallicoxidation catalysts and tannicacid have been proposed for this purpose.

In accordance with the present invention. it has been discovered thatmercaptan reduction in hydrocarbons is effectively increased by usinglignin in the aqueous alkali solution that is used to treat thehydrocarbon distillate, the alkali being treated with oxygen or anoxygen containing gas, such as air, at some stage during the process.

The process may be a single stage process, i. e., the hydrocarbons maybe treated with the llgnincontaining alkali in the presence of oxygen.The presence of the iignin assists in causing the solution of mercaptansin the caustic shifting equilibrium (l) to the right. The presence ofthe lignin also assists the oxygen in converting mercaptides tooxidation products, further shifting equilibrium (2) and (3) to theright. Generally the process is carried out in two steps in acoinmercial operation in which the lignin-containing caustic iscontacted with the mercaptan-containing hydrocarbon, and themercaptan-contalning and lignin-containing caustic is treated withoxygen to convert the mercaptans to oxidation products. The two-stepprocess is preferred and will be referred to hereinafter in describingthe invention.

The hydrocarbon material treated may be any containing mercaptans.Generally they are from petroleum sources and the materials mostcommonly treated are distillates, such as naphthas, gasoline, kerosene,etb.

Lignin is readily available as icy-products of processes involving theseparation of ceilulosic from non-cellulosic substances, such as thewaste liquors from chemical wood pulping processes.

aqueous alkali solution directly, or the lignin content may be isolatedfrom the waste liquors by acid precipitation and then added to thecaustic solution. Lignin derivatives, such as the disodlum salt or otheralkali metal salts, may be employed satisfactorily. Standardized gradesof llgnln are presently available commercially and it may be desirableto employ lignin of a uniform reproducible grade in carrying out thepresent invention.

The alkali solution to be used may be any of those normally employed forsuch purposes, such as caustic soda, caustic potash, alkali metalcarbonates, and other equivalent alkali compounds. The concentration ofthe caustic may be any concentration which will remove merca'ptans tothe desired extent. the preferred concentration being between 5 B. to 25as. (about 3 to 20%), the optimum strength being to in aqueous solution.

The lignin constituent may be employed in an amount sufficient tofacilitate mercaptan removal, concentrations of 0.5 to 10% beingsuitable, and amounts of 2 to 4% by weight of the caustic solution beingoptimum.

In carrying out the method of the present inmention, it is preferred toprewash the hydrocarbon distillate with caustic to remove the morereadily removable sulfur constituents, such as free sulfur and hydrogensulfide, thus avoiding undue sulfur contamination of the causticcontaining lignin, employed in the separation of the mercaptans. Themercaptan extraction is eflected at temperatures at which the mercaptanspass readily to the caustic phase, temperatures between F. and 200 F.being preferred and best results being obtained with a temperatureapproximating 100 F.

The mercaptan extraction with aqueous alkali solution, in a two-stepoperation, may be accomplished in any known way. In practice, it hasbeen found desirable to employ suillcient caustic to extract themercaptans to the desired extent, for example, 10 to 1000 volumes oicaustic with 100 volumes of hydrocarbon distillate, carrying the liquidsthrough a single stage or a counter current multi-stage extractionprocess, as desired, to effect removal of the mercaptans from thehydrocarbon distillate.

Suitable additives to aid in solution of the mercaptans in the caustic,other than the lignin, may be employed. It has been found thatadvantageous results are obtained by allowing natural cresol and xylol,components normally present in the hydrocarbon, to build up inconcentration in the caustic.

Oxidation of the mercaptans in the spent caustic containing the ligninmay be accomplished in any known manner, such as by passing oxygen or anoxygen-containing gas through the caustic solution. Advantageous resultsmay be obtained by use of superatmospheric pressures, although theadvantages of the invention are not limited to employment of thisexpedient. Pressures from atmospheric to 250 lbs. sq. in, have beenemployed satisfactorily.

The temperature at which the mercaptan oxidation step may be carried outshould be such as to accomplish removal of the mercaptans and atemperature of between 50 F. and 200 F. is satisfactory, desirableresults being obtained with a temperature of 125 F.

The following experimental data substantiates the effectiveness oflignin to facilitate the removal of mercaptans from the caustic. Incarrying out 4 the experiments, "Induiin A" is a commercially availablelignln product obtained by acidifying the waste liquor from a sulfateand soda paper pulp process, whereas "Indulin C" is the disodiumderivative of "Indulin A."

[All values in mine] Mercaptan Sulfur per Liter oi Caustic LigulnAdditive in l5% NaOH Moral tan Initial ono. ftcr Oxidation Mercanlb MinRate Per ton Cone. Treatment Min.

with Air None 8. 3 4. 2 27 4% "lndulin A" 8.3 1.3 .45 4% "lndulln C 8.30.0 .55 N one e o. 1.1 .7 .027 4% "Induiin C". I. l .18 .002

Mermptan Sulfur in Hgdrocarbon istillates Merca tan Lignln Additive in15% Noon Initial Mercaptan Extraction Per cent Per cent None 5% "lndulinC 0. 041

The above data show the efl'ectivcness of llgnln in facilitating theaction of the caustic in removing mercaptans from a hydrocarbondistillate such as gasoline.

It is not intended that the process of the resent invention be limitedto certain conditions of temperature and pressure hereinbeforedescribed, for the many variations possible in carrying out theinvention will be apparent to those skilled in the art.

We claim:

1. In a method of improving hydrocarbons the step of contacting amercaptan-containing hydrocarbon distillate in the liquid phase with anaqueous alkaline reagent having lignin dissolved therein.

2. In a'method of improving hydrocarbons the step of contacting amercaptan-containing hydrocarbon distillate in the liquid phase with anaqueous alkaline reagent having lignin dissolved therein in the presenceof oxygen.

3. In a method of improving mercaptan-containing hydrocarbon distillatein liquid phase by treating the same with an aqueous alkaline reagent,the step of contacting a mercaptan-contaming aqueous alkaline reagentwith oxygen in the presence of lignin dissolved therein, whereby theaqueous alkaline reagent may be recycled ior reuse in further treatingsaid hydrocarbon.

4. In a method oi improving hydrocarbons the steps of contacting amercaptan-containing hydrocarbon distillate in the liquid phase with an5 aqueous alkaline reagent having lignin dissolved therein to removemercaptans from the hydrocarbon, and treating the mercaptan-containingand lignin-containing alkaline reagent with oxygen to remove mercaptansfrom the reagent. whereby the aqueous alkaline treating reagent may berecycled to the hydrocarbon treating step.

5. In a method of improving hydrocarbons the steps of contacting amercaptan-contalning hydrocarbon distillate in the liquid phase with anaqueous alkaline reagent having lignin dissolved therein, separating thehydrocarbon from the alkaline reagent containing the mercaptan, toremove mercaptans from the hydrocarbon, and treating themercaptan-containing and lignincontaining alkaline reagent with oxygento remove mercaptans from the reagent, said lignin having been obtainedfrom a sulfate and soda pulp process, whereby the aqueous alkalinetreating reagent may be recycled to the hydrocarbon treating step.

6. In a method of improving hydrocarbons the steps of contacting amercaptan-containing hydrocarbon with an aqueous caustic solution havinglignin dissolved therein, separating the hydrocarbon from the causticsolution containing the mercaptan, to remove mercaptans from thehydrocarbon, and treating the mercaptan-containing and lignin-containingcaustic solution with oxygen to remove mercaptans from the reagent, saidlignin having been obtained from a sulfate and soda pulp process,whereby the aqueous alkaline treating reagent may be recycled to thehydrocarbon treating step.

7. In a method of improving hydrocarbons containing sulfur compounds,comprising contacting a hydrocarbon distillate in the liquid phase witha first alkaline solution to remove free sulfur and hydrogen sulfideconstituents normally present. and contacting the distillate with asecond aqueous alkaline solution having liznin dissolved therein, saidlignin having been obtained from av sulfate and soda pulp process.

ii. In a method of improving hydrocarbons the step of contacting amercaptan-containing hydrocarbon distillate in the liquid phase with anaqueous alkaline reagent having lignin dissolved therein, said ligninhaving been obtained from a sulfate and soda paper pulp process.

9. In a method of improving hydrocarbons the step of contacting amercaptan-containing hydrocarbon distillate in the liquid phase with anaqueous alkaline reagent having lignin dissolved therein, in thepresence of oxygen, said lignin having been obtained from a sulfate andsoda pap r Dull process.

10. In a method of improving mercaptan-containing hydrocarbon distillatein liquid phase by treating the same with an aqueous alkaline reagent,the step of contacting a mercaptan-containing aqueous alkaline reagentwith oxygen in the presence of lignin dissolved therein, said ligninhaving been obtained from a sulfate and soda paper pulp process, wherebythe aqueous alkaline reagent may be recycled for reuse in furthertreating said hydrocarbon.

ROBERT R. HIBBARD. FRANKLIN VEATCH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,015,038 Pevere Sept. 17, 19352,272,594 Bender Feb. 10, 1942 2,315,530 Loyd Apr. 6, 1943 2,317,054Henderson et al. Apr. 20, 1943 2,389,771 Bond Feb. 20, 1945 2,413,945Bolt Jan. '7, 1947 OTHER REFERENCES Gordon et al., Chlorine as aDeodorant Pulp Manufacture," Paper Trade Journal. April 28. 1938, pages81-85.

